The field of the invention is breathing gas systems employing a demand servomechanism to control or regulate the supply of breathing gas supplied to the user, and more particularly to an electronic servomechanism useful in a variety of applications and herein particularly useful for such a breathing system. The invention has significant utility in the fields of sport, scientific and commercial diving when scuba (self-contained underwater breathing apparatus) systems are employed, particularly as a replacement or substitute for the conventional demand servomechanism of the two stage, single hose regulator of an open circuit system. I prefer to denominate the entire apparatus an electronic scuba regulator or ESR.
Conventional mechanical scuba systems will be described only briefly. There are three categories of such systems: closed circuit; semi-closed circuit; and open circuit scuba. In the first two systems, the breathing medium is entirely reused or partially reused, after exhalation contaminants have been scrubbed. In open circuit systems, the breathing medium--compressed air in most cases--is exhausted into the surrounding water and is not reused at all. The embodiments of the invention disclosed in the following specification are particularly suited for open circuit scuba although the invention can certainly be used with semi-closed and closed systems.
There are two basic regulator designs in open circuit scuba. One is the two hose regulator and it may comprise one, two or more stages for reducing the tank pressure of the air supply down to a breathable, ambient pressure. The other design is a single hose regulator having two stages, most often. The first stage reduces pressure from the supply tank to a fixed pressure over ambient (usually 100-150 psi) and the second stage further reduces the pressure to breathable ambient pressure. Conventionally, the first stage is mounted on the valve assembly of the supply tank or tanks and the second stage includes a mouthpiece gripped by the user's teeth. A single relatively small diameter hose connects the two stages.
This second stage of a conventional, mechanical scuba regulator includes a demand valve, contact linked to a flexible diaphragm which defines one wall of a demand chamber or receiver unit. When the user breathes in through the aforementioned mouthpiece, a pressure differential or demand is created in the receiver. The diaphragm is thus caused to flex inwardly, due to relatively higher, outside ambient pressure. Subsequently, the demand valve of the second stage is opened, causing air to enter the receiver unit and thus flow to the mouthpiece and the user. Regardless of water depth, air is delivered on demand to the user since its supply and delivery is controlled by ambient pressure and user demand. Of course, if the pressure in the supply or tank falls to or below the ambient pressure, no air is delivered and the system is thus exhausted. The receiver unit is further equipped with one or more, one-way flap valves for exhaust purposes; upon exhalation, air is directed back through the receiver and out of the flap valve into the surrounding water.
A major drawback of the conventional, mechanical, two-stage single hose scuba regulator just described is the requirement for physical exertion or "demand" on the part of the diver or user in order to extract a breath from the system. While more modern engineering techniques have reduced the exertion levels required for both inhalation and exhalation down to rather acceptable levels, nevertheless an actual breathing resistance is felt, which increases with depth due to increasing density of the breathing air being delivered. Specifically, on inhalation, a diaphragm must be moved and a valve opened by force of inhalation. On exhalation, air must be forced back through a receiver unit into the surrounding water. Increasing air density with depth only compounds the difficulty.
Additionally, conventional second stages are rather bulky and fatigue the user's mouth after a period of use. Failures of the unit are rare but have occurred, leaving the diver at depth either without air at all or with a high pressure stream jetting through the second stage. A fractured or displaced diaphragm and/or malfunctioning exhaust valve can render the receiver unit full of water and dangerously unusable.
In summary, several significant deficiencies of mechanical scuba regulators can be noted:
(1) Significant breathing resistance, particularly under conditions of increased air density (greater depth);
(2) Excessive mouth-vicinity mass;
(3) Diaphragm size and fragility;
(4) Dangerous and unsafe under conditions of failure.
Representative prior art disclosures of mechanical scuba regulators are found in U.S. Pat. Nos. 2,523,906; 2,728,340; 2,854,001; 2,894,506; 2,902,031; 3,028,860 and 3,480,011.
The next advance in the art was to develop an electromechanical regulator that would overcome at least some of the noted breathing resistance problems, on inhalation and exhalation. The following three patents deal with regulator systems unrelated to diving, however. These include U.S. Pat. Nos. 3,368,212; 3,500,826 and 3,611,178. U.S. Pat. No. 3,368,212 issued to S. D. Klyce is simply a monitoring system, designed for use with an ill patient and includes an alarm system which is actuated when the patient's breathing rate falls below a predetermined value. U.S. Pat. No. 3,500,826 issued to C. A. Haire concerns an O.sub.2 mask for an air-crew member employing a differential pressure transducer to read demand and a single solenoid actuator for providing O.sub.2 in response to demand, the displacement of the solenoid plunger being continuously governed by the magnitude of current flowing in the coil, which in turn is controlled by the differential pressure transducer. U.S. Pat. No. 3,611,178 discloses an electrical assist for a respirator designed primarily for hospital use including a diaphragm with electrical means to sense demand and activate the respirator in response to such demand. In short, the invention therein disclosed is an electrical pilot valve. Prior U.S. Pat. Nos. 3,523,677; 3,586,287; 3,625,477; 3,770,018 and 3,817,488 each disclose electropneumatic devices or electromagnetic gas valves. U.S. Pat. No. 3,695,261 discloses means for converting a conventional open circuit scuba rig into a semi-closed system by incorporating an electronically controlled rebreather system and U.S. Pat. No. 3,794,059 discloses a closed or semi-closed scuba system employing an electronic monitoring control and display system in the breathing gas supply system.
However, the prior art fails to disclose the use of sensor technology in providing a power assist to the demand element in an underwater breathing apparatus. The present invention is further directed to providing electronic assistance to breathing in the underwater domain.